The invention concerns a method and arrangement for automatic detection of operating voltage, in which a selection of an internal power supply voltage occurs from at least two different external power supply voltages, a first external power supply voltage being permanently applied.
For example, methods and arrangements for automatic detection of operating voltage are known from GB 2 402 004, US 2004/0222840, JP 2004234540 and EP 1 163 571.
The drawbacks of these methods and arrangements consist of the fact that either a microprocessor is required for control or an analog circuit part is used, which leads to an increase in current demand by the overall arrangement. Another drawback is that the two different external power supply voltages must be in a specific ratio to each other.
The task of the invention therefore consists of reducing the circuit cost for automatic detection of operating voltage, the operating current caused by the selection arrangement and the required chip surface, in which the voltage ratios of the two different power supply voltages can be arbitrary relative to each other.
The solution to the task according to the invention on the method side is implemented by the features of Claim 1.